1. Field of the Invention
This invention relates to an edge detecting apparatus and method for detecting an edge, which is located between pixels constituting an image, for use in, for example, processing for enlarging or reducing a size of the image represented by an image signal. This invention also relates to a profile judging apparatus and method for making a judgment as to a shape of a profile of values of pixels constituting an image. This invention further relates to an image size enlarging and reducing apparatus and method for enlarging and reducing a size of an image represented by an image signal. This invention still further relates to an image interpolation apparatus and method for interpolating a new pixel between pixels, which constitute an image, for use in processing for enlarging or reducing a size of the image represented by an image signal. This invention also relates to a computer program for causing a computer to execute the edge detecting method, the profile judging method, the image size enlarging and reducing method, or the image interpolation method. This invention further relates to a computer readable recording medium, on which the computer program has been recorded.
2. Description of the Related Art
Operations have heretofore been conducted, wherein an image signal, which has been obtained from a photoelectric readout of an image having been recorded on photographic film, or an image signal, which has been obtained from the imaging of an object with an imaging device, such as a digital camera or a portable telephone with camera, is subjected to processing for enlarging or reducing the size of the image represented by the image signal, such that the size of the image may be adapted to the size of a monitor utilized for reproducing the image from the image signal. In particular, services have heretofore been furnished wherein, at the time of sending of the image signal, which has been obtained from the imaging of the object with the portable telephone with camera, as electronic mail, the image signal is subjected to the processing for enlarging or reducing the size of the image represented by the image signal in accordance with the size of the liquid crystal monitor of the portable telephone to which the image signal is to be sent.
The image size enlargement or reduction processing on the image signal is performed with the processing, wherein a new pixel is interpolated between the pixels, which constitute the image represented by the image signal, in accordance with an enlargement scale factor. As techniques for interpolating the new pixel, various techniques, such as a linear interpolation technique, a nearest neighbor interpolation technique, a bilinear technique, and a bicubic technique, have heretofore been known.
Also, there has been proposed a technique, wherein a pixel (a pixel of interest), which is located at the position closest to the position of a new pixel, and adjacent pixels, which are adjacent to the pixel of interest, are selected, a difference value between the values of the adjacent pixels, which are located with the pixel of interest intervening therebetween, is calculated, a correction value is calculated in accordance with the difference value and a distance between the pixel of interest and the new pixel, and a pixel value of the new pixel is calculated in accordance with the pixel value of the pixel of interest, the difference value, and the correction value. (The technique described above is disclosed in, for example, U.S. Patent Laid-Open No. 20010787277.)
However, in cases where the image size enlargement or reduction processing on the image signal is performed with a single technique alone, the problems occur in that an edge area contained in the image is blurred or becomes shaggy. Therefore, a technique for detecting an edge component contained in an image and performing interpolating operations, in which different interpolating operation processes are utilized for the edge area and a non-edge area. (The technique described above is disclosed in, for example, Japanese Unexamined Patent Publication No. 2002-319020.)
In order for the edge to be detected from the image in the technique disclosed in Japanese Unexamined Patent Publication No. 2002-319020, or the like, a Sobel filter or a Laplacian filter is ordinarily utilized. Each of the Sobel filter and the Laplacian filter has an odd number of taps, e.g. three taps. With the filtering processing performed by use of the sobel filter or the Laplacian filter, a judgment is made as to whether a pixel of interest is or is not a pixel constituting an edge in an image, and the edge in the image is thus capable of being detected.
In cases where the image size enlargement or reduction processing is performed on an image, since a new pixel is to be interpolated between pixels, instead of a judgment being made as to whether an edge in an image is located at a pixel contained in the image, it is necessary that a judgment be made as to whether an edge in an image is or is not located between pixels. However, in cases where the detection of an edge is performed by use of the aforesaid filter having an odd number of the taps, a judgment is capable of being made merely as to whether a pixel of interest itself in an image is or is not a pixel constituting the edge in the image, and a judgment is not capable of being made as to whether an edge in the image is or is not located between pixels.
Also, with the aforesaid technique disclosed in Japanese Unexamined Patent Publication No. 2002-319020, the interpolating operations are performed, in which different interpolating operation processes are utilized for the edge area and the non-edge area. However, the known techniques described above are utilized as the interpolating operation processes, and therefore the problems still occur in that the edge area is blurred. For example, in cases where four pixels G1, G2, G3, and G4, which are adjacent in series to one another, have the shape of the profile as illustrated in FIG. 37A, a sharp edge is located between the pixel G2 and the pixel G3. Also, in cases where four pixels G1, G2, G3, and G4, which are adjacent in series to one another, have the shape of the profile as illustrated in FIG. 37B, an edge is located between the pixel G2 and the pixel G3. In the example illustrated in FIG. 37A or FIG. 37B, in cases where a pixel value of an interpolated pixel between the pixel G2 and the pixel G3 is calculated by use of, for example, the linear interpolation technique, a value lying on the straight line connecting the pixel G2 and the pixel G3, which are located in the vicinity of the interpolated pixel, is taken as the pixel value of the interpolated pixel. Therefore, regardless of the presence of the edge between the pixel G2 and the pixel G3, the variation in pixel value in the vicinity of the edge becomes smooth. As a result, the edge area in the image obtained from the image size enlargement or reduction processing becomes blurred.
Further, with the aforesaid various techniques, such as the linear interpolation technique, the nearest neighbor interpolation technique, the bilinear technique, and the bicubic technique, the pixel value of the new pixel is calculated by the utilization of the pixel values of the pixels, which are distributed in two-dimensional directions in the vicinity of the new pixel. Therefore, a long time is required to perform the interpolating operation.
Furthermore, with the aforesaid various techniques for the interpolation of the new pixel, in cases where an edge is located in the vicinity of the new pixel, the pixel value of the new pixel is calculated from the pixel value of a pixel, which is located on the edge, and the pixel value of a pixel, which is located at a position other than the edge. Therefore, the problems occur in that the edge area in the image obtained from the image size enlargement or reduction processing becomes blurred.